Electronegativity describes the degree to which an atom attracts electrons in a chemical bond. The difference in the electronegativity of two atoms determines their bond type. If the electronegativity difference is more than 1.7, the bond will have an ionic character. If the electronegativity difference is between 0.4 and 1.7, the bond will have a polar covalent character. Lastly, if the electronegativity difference is less than 0.4, the bond will have a nonpolar covalent character.

The Concept of Electronegativity

Unlike many other periodic trends, electronegativity does not have actual units. Instead, it is a way of combining two other periodic trends: ionization energy and electron affinity. Ionization energy is the amount of energy required to remove an electron from a neutral atom. Electron affinity is the amount of energy given off or required when a neutral atom gains an electron. Electronegativity does not have any units. However, the Pauling scale for electronegativity lists cesium as the least electronegative element, with a value of 0.79. In this scale, fluorine is the most electronegative element, with a value of 4.0.

Sodium Chloride, an Ionic Bond

Sodium has an electronegativity of 0.9, while chlorine has an electronegativity of 3.0. The difference between these values is 2.1, which means that sodium chloride has an ionic bond. In an ionic bond, the more electronegative element will attract an electron from the less electronegative element. In this case, chlorine becomes a Cl- ion, while sodium becomes an Na+ ion.

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Water, a Polar Bond

Hydrogen has an electronegativity of 2.0, while oxygen has an electronegativity of 3.5. The difference in electronegativities is 1.5, which means that water is a polar covalent molecule. This means that the electrons are drawn significantly towards the more electronegative element, but the atoms do not become ionized. In water, an electron from each of the hydrogen atoms is drawn towards the oxygen atom. In this case, the oxygen atom has a partial negative charge, whereas the hydrogen atoms have partial positive charges.

Hydrogen Gas, a Covalent Bond

In hydrogen gas, two hydrogen atoms bond together. The electronegativity difference between these atoms is zero. This is a nonpolar covalent bond. In this case, the electrons of the two atoms do not favor one atom over the other. Instead, they orbit both nuclei and are said to be shared between the two atoms. Covalent bonds can exist between two different elements as well, as long as their electronegativity difference is less than 0.4.

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About the Author

Serm Murmson is a writer, thinker, musician and many other things. He has a bachelor's degree in anthropology from the University of Chicago. His concerns include such things as categories, language, descriptions, representation, criticism and labor. He has been writing professionally since 2008.